Pocket air filters are used to clean air, where several filter bags are usually arranged at a distance from each other in the pocket air filter. In order to clean a current of air, the pocket air filter is located in the air stream in such a way that air flows through the side parts of the filter bags from the respective opening side and particles contained in the air are separated out at the side portions.
In order to achieve the best possible filter effect and to make maximum possible use of the filter area formed by the side parts, the filter bags are normally designed in such a way that the air flows evenly through the entire filter area. For this purpose, it is necessary to adjust the distance between the filter bags of a pocket air filter and, in particular, to prevent side parts of adjacent filter bags from making contact with each other, as this would severely reduce the effective filter area.
Therefore, the cross-section of conventional filter bags usually runs from the opening to the bottom edge, whereby the cross-section is continuously reduced. This is achieved by the connection between the opposing side parts of a filter bag by the webs, by which the distance between the side walls of a filter bag and, thereby indirectly, also the distance between this filter bag and a filter bag arranged adjacently in the pocket air filter, can be specified.
A manufacturing process for such filter bags is described in document EP 1 049 527 B1. In the case of the process described in this document, the filter bags are manufactured from two webs of filter material and the flexible material web. These webs run into a suitable welding unit, where the flexible material web is arranged between the filter material webs and is fed to the welding device.
The welding device has several sonotrodes, with which the filter material webs and the flexible material web can be welded together by ultrasound. In order to weld only one of the filter material webs to the flexible material web alternately, the welding device also has transferrable plates, which are arranged between the flexible material web and the filter material webs so as to be transferrable and prevent the flexible material web from being welded to the filter material web, which is separated from the flexible material web during welding by a plate. By alternately welding the flexible material web to the two filter material webs, webs are formed between the filter material webs from the flexible material of the material web.
In order to facilitate a continuously reducing distance between the side parts by the webs from the opening side to the bottom edge, it is necessary that the web portion width or web width of the web portion or webs decreases from the opening side towards the bottom edge. This is achieved by the filter bags known from the state of the art, in that adjacent welding portions, with which the flexible material web is welded in each case to one of the side parts, are more widely spaced apart on one side of the welding portions facing the opening side, than on a side facing the bottom edge.
In order also to facilitate a corresponding space between the side parts in the area of the side edges of the filter bag, it is also provided in the case of the filter bags known from the state of the art, that the side parts are developed to be trapezoidal, so that a space between the side edges and weld portions arranged in each case adjacent to the side edges, likewise decreases from the opening side towards the bottom edge. The trapezoidal development means that a web portion is also formed, which has a decreasing web portion width, as a result of the flexible material web between the outermost weld portions and the side edges, to which both side parts are welded together and to the flexible material web. The filter area available is reduced as a result of the necessarily trapezoidal design of the filter bags.
The side parts of high-quality filter bags also have a trapezoidal shape for different reasons, as for example to facilitate installation. However, an angle between the side edges or with the bottom edge is largely determined by the required cross-sectional shape of the filter bags in the condition where they are installed and air is passing through or in the installed position.
It is regarded as the task of the disclosure to provide a filter bag for pocket air filters, where the filter area available for filtering can be enlarged.